Question

Question No. 45
Behind a thin converging lens having both the surface of the same radius 10cm, a plane miror has been placed. The image of an object at a
distance 40 cm from the lens is formed at same position. What is the refractive index of lens?​

Answer 1

Hence the refractive index of the lens is μ = 9 / 8

Explanation:

• Radius of lens = 10 cm
• Distance of object = 40 cm
• To Find: Refractive index of the kens "n" = ?

Solution:

Using lens mirror formula;

1/ f = ( μ−1 ) ( 1/ R1 - 1/ R2 )

=>  1/ 40 =  ( μ−1 )  ( 1/ 10 + 1/ 10)

1 / 40 =  ( μ−1 ) 2 / 10

1 =  ( μ−1 ) 2 / 10 x 40

1 =  ( μ−1 )  2  x 4

1 =  ( μ−1 )  8

1 = 8 μ - 8

μ = 9 / 8

Hence the refractive index of the lens is μ = 9 / 8